update_category_budget · YNAB MCP Server MCP: Risk & Policy

WHAT IT DOES

What update_category_budget does on YNAB MCP Server

AI agents use update_category_budget to create or update resources in YNAB MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your YNAB MCP Server environment.

WHY IT NEEDS A POLICY

Why update_category_budget needs a policy

This tool modifies financial planning data (category budgets) but does not move money, delete data, or execute arbitrary code. It is reversible—a budgeted amount can be changed again. However, severity is elevated to 'high' because misuse could lead to incorrect budget allocations that cause financial planning errors, though the actual financial accounts/transactions remain intact.

From the tool's definition Tool name 'update_category_budget' and description 'Update the budgeted amount for a category in a specific month' indicate modification of budget data. The verb 'Update' directly shows reversible data modification.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_category_budget Rate-limited

update_category_budget stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "update_category_budget": {
      "limits": [
        {
          "counter": "update_category_budget_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches YNAB MCP Server, so you can run agents against it safely.

FAQ

Questions about update_category_budget

What does the update_category_budget tool do? +

Update the budgeted amount for a category in a specific month. It is categorised as a Write tool in the YNAB MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_category_budget? +

Register the YNAB MCP Server MCP server in PolicyLayer and add a rule for update_category_budget: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches YNAB MCP Server. Nothing to install.

What risk level is update_category_budget? +

update_category_budget is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit update_category_budget? +

Yes. Add a rate_limit block to the update_category_budget rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block update_category_budget completely? +

Set action: deny in the PolicyLayer policy for update_category_budget. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides update_category_budget? +

update_category_budget is provided by the YNAB MCP Server MCP server (jeangnc/ynab-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.